J. Neurol. Neurosurg. Psychiat., 1965, 28, 311

Facial nerve preservation by posterior fossatransmeatal microdissection in total

removal of acoustic tumoursR. W. RAND AND T. L. KURZE

From the Divisions of Neurological Surgery, School of Medicine, University of California, Los Angeles, andUniversity of Southern California, School of Medicine, U.S.A.

Intracranial preservation or reconstruction of thefacial nerve during total removal of acoustic tumourshas infrequently been possible heretofore, the facialnerve being preserved in only 10% to 32% of opera-tions performed by neurosurgeons (Bucy, 1951;Dandy, 1941; Dott, 1955, 1958; Drake, 1960;Horrax, 1950; Nielsen, 1942; Pool and Pava, 1957;Revilla, 1947; Olivecrona, 1950). The need forimproved surgical techniques to prevent facial palsyin the majority of cases in which a tumour has beenwholly removed has been recognized for many yearsand was emphasized by Pool and Pava in 1957: 'Theproblem stemming from facial nerve involvement isof considerable importance if only because of itspsychological ramifications. It may become moreacute if the corneal anaesthesia should be alsopresent.'McKenzie and Alexander (1955) concentrated on

performing total removal, including the intrameatalportion of acoustic tumours, and made no particulareffort to save the facial nerve. They pointed out thatit was more important to cure the younger patientthan to preserve the facial nerve. It is well knownthat total removal of acoustic neurinomas afterrecurrence is extremely difficult (Ransohoff,Potanos, Boschenstein, and Pool, 1961). Facialhypoglossal nerve anastamosis was done at a laterstage with satisfactory restoration of facial tone andsymmetry.The posterior fossa transmeatal approach to be

described here does permit the facial nerve either tobe preserved during removal of the whole of theacoustic tumour, or reconstructed with or withoutan intracranial nerve graft should this be necessary.In order to carry out such dissection the binocularsurgical microscope is required.

This approach also provides ready access to thenormal contents of the internal auditory canal forselective section of the superior or the inferiorvestibular nerve without sacrificing the cochlear orthe facial nerves.

OPERATIVE TECHNIQUE

The sitting posture with hypothermia to 300 C. undergeneral anaesthesia has been employed (Rand, 1957).The patient's head is held in a specially designed unitwith four-point skull fixation above the ears and supra-orbital ridges, respectively. This unit allows head flexionduring the opening and the resective stages of the oper-ation, and head extension for wound closure withouttension.A unilateral incision is started below the tip of the

mastoid process passing above the attachment of the sub-occipital muscles to end in a vertical limb in the mid-cervical area (McKenzie and Alexander, 1955). A strip offascia and muscle is left attached to the superior nuchalline to provide for tight closure. A generous unilateralcraniectomy in large tumours includes the bone superiorto the lateral sinus, the ipsilateral side of the foramenmagnum, and the region anterolateral to the mastoidcells. A paramedian incision may be used and the wall ofthe foramen magnum may be left intact when the cere-bello-pontine angle tumour is small (Bucy, 1951).Especially with small tumours the half axial prone posturemay be useful (Mount, 1945). This allows the cerebellumto fall away from the tumour by gravity and with mildretraction.The dura is opened in a cruciate design and its flaps are

sutured to the wound edges or it may be opened aroundthe edge of the craniectomy leaving dura covering thecerebellum. In the sitting posture, the cerebellar hemi-sphere hangs down in a loose fashion due to shrinkagefrom the use of hypothermia, and intravenous urea ormannitol, which is started slowly at the beginning of theprocedure. The systolic blood pressure is not allowed tofall below 100 mm. of mercury. Transfusion is com-menced at the beginning of the operation, allowingvolume-for-volume replacement.

In order to lessen postoperative swelling and avoid airembolism, care must be taken not to damage the superiorveins draining the cerebellum. The cerebellum is retractedgently upward without compressing the brain-stem,using a self-retaining retractor. In this way, access to theentire lateral wall of the posterior fossa and cerebello-pontine angle is gained. The jugular and acoustic fora-men and their contents are readily identified grossly and

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especially well with the binocular operating microscope.The lateral portion of the cerebellar hemisphere is notresected. If the acoustic tumour is especially large a por-tion of it may be removed to expose the edge of theporus acousticus.

Care is taken to preserve the arachnoid over thelower cranial nerves. Only a small opening is made in thecisterna magna to allow for cerebrospinal fluid drainage.Thus, any bone debris from drilling and blood whichescapes suction will not get into the subarachnoid spaceand can be irrigated away.The dura mater over the posterior superior wall of the

porus acousticus is carefully coagulated under magnifica-tion of the surgical microscope after identifying thetumour. It is removed from the bone with sharp curettes.Drill dissection is used to eradicate the posterior andsuperior walls of the internal auditory canal. The cuttingdrill may be employed until soft tissue is approached andthen diamond drills, which do not cut soft tissue, aresubstituted. A combination irrigation-suction instrumentis used during the drilling to remove bone dust and to coolthe bone. The use of cottonoid strips and pledgets in theimmediate area of drill dissection must be avoided becausethey may be caught in the drill. The wall of the porusacousticus is removed laterally, preserving the tumourcapsule, until the origin of the tumour is visualized.One can identify the superior and inferior vestibularnerves through the microscope which are usually involvedto a greater or lesser extent in the origin of the tumour.With careful dissection between these nerve fibres, thecochlear nerve can be seen anteriorly and inferiorly.It may be saved in certain cases of small tumour if it isnot directly involved.

In the most antero-superior portion of the internalauditory canal, the facial nerve will be found to be freeof the tumour capsule. Confirmation may be obtained bydirect electrical stimulation and observation of facialmovements. The neurinoma is then gently teased out ofthe canal with curettage, suction, and cup forceps aftercutting the vestibular nerves lateral to the origin of thetumour. The tumour capsule is separated from the facialnerve by continued gentle, sharp and blunt dissectionunder the surgical microscope; Excessive mechanicalstretching will usually result in facial movements easilyobserved by the anaesthetist. The air cells in the petrousbone may then be sealed with bone wax, gelfoam, ormuscle stamp to prevent cerebrospinal fluid otorrhoea.Once the internal auditory canal is cleared of the

tumour, attention is directed to decompressing the tumour(Cushing, 1917), if necessary, by internal curettage,suction and/or an electrosurgical loop. As the tumourmass is decreased in size, the capsule is grasped gentlywith cup forceps and the cleavage plane between thetumour and the brain-stem is identified. At this point,the major vessels passing from the brain-stem to thetumour can be seen and dissected from the capsule,bluntly or by using small cottonoid sponges. Only thosevessels intimately supplying blood to the tumour arecarefully coagulated and transected. Care is taken not todamage the anterior inferior cerebellar artery and itsbranches, which can also be observed under the micro-scope. The eighth nerve may need to be sectioned on the

mesial side of small tumours. Care must be taken toidentify the facial nerve before this step is taken. Theinferior pole of the tumour is thus freed from the brain-stem and lower cranial nerves.

Attention is then directed superiorly, keeping the facialnerve identified as the capsule is removed carefully fromit. The residual tumour is lifted from the brain-stem. Withsmall neoplasms, one can identify and separate all vascu-lar structures as well as the seventh nerve from theneurinoma without great difficulty (case 1). With largertumours, the problem becomes increasingly moredifficult, and consequently the seventh nerve may besacrificed during total tumour resection, either becauseof thinning and adherence to the capsule (case 2) or directinvasion by the tumour (case 3). In these instances, withthe use of microneurosurgical techniques, reconstruc-tion can be accomplished using 6-0 to 8-0 black silksutures.

Following resection of the tumour, the posterior fossais searched carefully for bleeding points, which arecoagulated and a watertight closure of the dura is ac-complished. The fascia, muscles, and scalp layers of thewound are sutured anatomically in the usual mannerwithout tension or drainage.

CASE REPORTS

The posterior fossa transmeatal approach usingmicroneurosurgical techniques was performed suc-cessfully on three patients with small to largeacoustic tumours.

CASE 1 The patient, a 49-year-old, right-handed house-wife, had had a roaring sound and sense of fullness inher right ear since 1961, followed by progressively de-creasing hearing in that ear since early 1962.The findings of the neurological examination were

limited to the loss of hearing in the right ear with slightintention tremor in the outstretched hands.

Otological investigations showed a profound rightsensorineural hearing loss with some recruitment in thehigher frequencies. Bekesy audiometry was type IV.The caloric tests were inconclusive.

Neuroradiological studies of the skull, includingplanigrams, demonstrated that the right porus acousticuswas not eroded. The positive contrast study of the cere-bellopontine angle cistern showed a small acoustictumour 1-8 cm. in diameter on the right side (Fig. 1).At operation on 1 May 1964, it was possible to dissect

the tumour from the right porus acousticus in the mannerdescribed, preserving the seventh nerve throughout itsentire distance (Fig. 2). The tumour apparently arosefrom the inferior vestibular nerve. The anterior inferiorcerebellar artery was identified and cleared from thecapsule except at one small point where it densely adhered.The capsule was left at this point to avoid damage to theartery. It was necessary to cut the proximal end of thevestibular and cochlear divisions of the acoustic nerveto deliver the tumour from the brain-stem.The patient's postoperative course was uneventful,

although she developed a partial facial palsy which

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Facial nervepreservation byposteriorfossa transmeatal microdissection in total removal ofacoustic tumours 313

FIG. 1. Radiograph ofpositive contrast study of right cere-bellopontine angle in case 1: (A) small acoustic tumourdefect; (B) cerebellar tonsildefect; (c) vertebral andposteriorinferior cerebellar arteries; (D) trigeminal nerve defect.

FIG. 2. Photograph through surgical microscope afterresection of acoustic tumour in case 1: (A) residual neuri-noma within porus acousticus removed after furtherunroofing of the canal by a diamond burr; (B) facial nerveintact; (c) anterior-inferior cerebellar artery; (D) brain-stem and cerebellum.

gradually became complete within 24 hours. Four monthsafter surgery partial facial muscle function had re-turned and was nearly normal seven months afteroperation.

CASE 2 The patient, a 41-year-old, right-handed woman,had complaints of pulsations in the right ear, followedby tinnitus and mild deafness since 1963. The symptomscontinued in addition to her developing some numbnessin the right side of her teeth and tongue.

Neurological examination demonstrated a mildvariable internal strabismus without specific muscleparesis, mild horizontal nystagmus on gaze to right orleft, mild hypaesthesia, and hypalgesia of the entire rightside of the face, decrease of right comeal response, someweakness of the left side of the face at rest and decreasedhearing on the right side. Mild unsteadiness on heel toshin testing on the right lower extremity waspresent.The otological studies demonstrated sensori-neural

hearing loss on the right with recruitment at high fre-quencies only. Bekesy audiometry was type IV. Thecaloric tests were equivocal.

Neuroradiological studies of the skull, includingplanigrams, demonstrated that the right porus acousticuswas eroded. A cerebellopontine angle positive contrast

FIG. 3. Photograph of positive contrast study of rightcerebellopontine angle with defect due to acoustic tumourin case 2 (arrow). Note enlargedporus acousticus in centrearea of defect.

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FIG. 4. Reconstruction offacial nerve by direct suture as

seen through surgical microscope in case 2.

myelogram showed a large tumour 3 5 x 2 cm. (Fig. 3),confirming the clinical diagnosis.At operation on 18 May 1964 the tumour was found

to be massive, extending through the right side of theincisura compressing the brain-stem. It arose primarilyfrom the inferior vestibular nerve. The seventh nerve was

traced from the porus acousticus into the capsule of thetumour and from the brain-stem into the capsule where itwas thinned out and severed as the neoplasm was beingtotally removed. The proximal and distal ends were identi-fied and sutured with 6-0 silk (Fig. 4).

Postoperatively a tarsorrhaphy was carried out becauseof the corneal hypalgesia and the complete seventh nervepalsy on the right. Other neurological symptoms dis-appeared. The facial palsy remained complete at the eight

months postoperative follow-up. Physiotherapy andgalvanic stimulation of the muscles is being continued.If facial function does not begin to return after one year afacial-hypoglossal nerve anastamosis will be performed.

CASE 3 The patient was a 40-year-old pharmacist who,10 years previously, had several illnesses apparently dueto multiple sclerosis. The symptoms at that time involvedprimarily the spinal cord systems and optic nerves. In1961 he developed a progressive loss of hearing in the leftear superimposed upon the sequelae of his multiplesclerosis.

Neurological examination demonstrated mild cortico-spinal and cerebellar pathway findings, which werethought to be the result of previous disease. These con-sisted of a somewhat spastic-ataxic gait with hyperactivereflexes. In addition, there was loss of hearing on the leftside.

Audiological studies showed a sensori-neural loss onthe left with recruitment. Bekesy audiometry was type II.Caloric responses were abnormal on the left.

Neuroradiological findings revealed an erosion of theleft porus acousticus and a moderate sized left acoustictumour, 3 x 2-5 cm. in diameter, shown in the cerebello-pontine angle positive contrast study.

Operation on 24 July 1964 started with dissection inthe porus acousticus. The seventh nerve was freed fromthe tumour which arose from the vestibular nerve. Thenerve was firmly adherent to the anterior inferior surfaceof the tumour. Eventually as resection of the tumour wascarried further it was found that this portion of the facialnerve was invaded by the neoplasm. Consequently, thissegment of nerve was resected and direct anastomosiswas performed after total tumour removal was com-pleted.The patient required a tracheostomy in the third post-

operative day, due to tracheo-bronchial infection andpneumonitis; this cleared under appropriate antibioticsand the site healed in a normal fashion. Tarsorrhaphywas used because of the facial palsy and decreased sensa-

FIG. 5 Photographs offacialexpressions seven months after totalremoval of acoustic tumour andprimaryintracranial facial nerve anastomosis(case 3). The tarsorrhaphy will bereleased when additional strengthreturns to the obicularis oculae muscle.

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tion in the cornea on the left side. Return of facial nervefunction was first evident in the cheek five months afteroperation and has continued to improve about the eyeand lower face.

DISCUSSION

Improved and expanded otological tests makepossible earlier diagnosis of acoustic tumours asshown by a recently published monograph editedby House (1964). Pure tone loss patterns and Hall-pike caloric tests were abnormal in slightly over 90%of these cases. Speech discrimination was abnormalin 69%. Bekesy audiometry was type III or IV in70%. Recruitment was absent or partial in 81 %and short increment sensitivity index (SISI test)scores were low in 70 %.The posterior fossa cerebellopontine angle cistern

positive contrast myelographic techniques perfectedby Scanlan (1964) and demonstrated in Figures 1and 3 were diagnostic of acoustic tumour in 95%of this series. The only negative study was in anintracanalicular acoustic tumour. Even these maybe detected now with additional special views of thecerebellopontine angle cistern and the internalauditory canal.An acoustic tumour arising from the internal

auditory canal can be approached from three direc-tions: (1) the subtemporal extradural middle fossa,(2) translabyrinthine, and (3) the transmeatalposterior fossa described here.Kurze (1958) was the first to advocate the middle

fossa extradural approach and a number of acoustictumours were totally removed in this manner (House,1964; Kurze and Doyle, 1962). The standard Spiller-Frazier craniectomy was performed and the greatersuperficial petrossal nerve identified using extraduraldissection. The canal of this nerve was unroofed bydiamond burr dissection to the geniculate ganglia ofthe facial nerve. The seventh nerve was further un-roofed by drill dissection between the labyrinthand the cochlea into the internal auditory canal.The major disadvantages to this approach are (1)the tedious and precarious diamond burr bonedissection to expose the facial nerve; (2) the limitedfield of exposure of the tumour even with removalof the labyrinth; and (3) the interposition of thetumour between the brain-stem vessels and thesurgical field.The translabyrinthine approach originally postu-

lated by Panse (1904) was perfected by House(1964). A partial mastoidectomy and total labyrinth-ectomy are carried out, exposing the internal audi-tory canal in the limited area between the jugularbulb, the sigmoid sinus, the fallopian canal of thefacial nerve, and the superior petrossal sinus. The

cerebellopontine angle is then further exposed bypartially opening the dura mater lining the posteriorfossa adjacent to the cerebellum. The tumour isremoved piecemeal.

Forty-four per cent of tumour resections by thisroute were necessarily partial because of the sizeof the tumour, intimate attachment of the neoplasmto the anterior inferior cerebellar artery and/orbrain-stem, and haemorrhage. However, of the 23tumours totally removed no residual damage of thefacial nerve function was observed in 56-5 %.Mild to severe weakness was present in the remaining10 cases. It is apparent that these results of facialnerve preservation represent a distinct improvementcompared with most past neurosurgical efforts(Nielsen, 1942). However, a significant number ofthese benign and curable tumours were not removedtotally by this technique.The major disadvantages of this approach to the

internal auditory canal are similar to the middlefossa exposure and include (1) the limited field ofaction, (2) the production of total hearing loss beforethe tumour is directly identified, (3) inability toobserve and dissect directly the tumour capsulefrom the brain-stem and its vessels, especially theanterior inferior cerebellar artery, and (4) increasedrisk of cerebrospinal fluid otorrhoea.A technique for total removal of an acoustic

tumour was developed by Dandy in 1925 and hasincontestable advantages, not available by the othermethods of approach. The unilateral posterior fossasuboccipital craniectomy was employed. Unroofingof the porus acousticus was advocated to ensuretotal removal of the acoustic tumour within thecanal. Preservation of the seventh nerve was limitedto approximately 10% in his series.From the experiences with the subtemporal middle

fossa extradural approach, it was found that thefacial nerve was most free from the acoustic tumourcapsule in the lateral portion of the internal audi-tory canal. And we have found by extensively un-roofing the porous acousticus via the posterior fossa,using drill dissection under the binocular surgicalmicroscope, that the facial nerve can be left un-disturbed in the internal auditory canal while theintrameatal portion of the acoustic tumour is beingresected. It is not necessary to open the labyrinth.The remaining tumour is reduced in size by aCushing type internal decompression (Cushing,1917) after this initial step, and then the capsule ismicrodissected from the brain-stem, its vessels andthe intracranial portion of the seventh nerve. Withthis approach, in contrast to the aforementioned,the entire dissection of the tumour can be doneunder direct vision and only those small vessels in-volving the capsule are sacrificed. The anterior

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inferior cerebellar artery and lower cranial nervesare readily identified and preserved without inter-position of the tumour to obscure vision.

In the past, the lateral portion of the cerebellarhemisphere was often resected, but this is no longernecessary with the use of intravenous urea, mannitol,and drainage of the cerebrospinal fluid. The singledisadvantage of this technique is cerebellar retrac-tion which is relatively unnecessary in the trans-labyrinthine and middle fossa approaches to theinternal auditory canal.The advantages of the posterior fossa transmeatal

technique over the extradural middle fossa and trans-labyrinthine approaches may be summarized asfollows: (1) a wide field of action; (2) immediateand direct visualization of the anterior inferiorcerebellar artery; (3) identification of the acoustictumour before risk of damage of the facial nerve,the labyrinth, and cochlear systems; (4) dissectionof the tumour is always under direct vision; and (5)direct anastomosis or reconstruction with nervegraft of the facial nerve is permitted when necessary.

SUMMARY

The principles of preservation or reconstruction ofthe facial nerve with microneurosurgical techniquesduring total removal of variously sized acoustictumours through the posterior fossa approach aredescribed.Three consectuve cases of acoustic tumour are

presented in which the facial nerve was preservedin one and reconstructed in two after total removal.Facial muscle function has partly returned in onepatient following anastomosis.

This technique appears to incorporate all of theadvantages of previously described techniques foracoustic tumour resection and avoids their dis-advantages.

ADDENDUM

Since the commencement of our work and ourreview of the literature, the article by Rougerie andGuyot (1964) has come to our attention. The sur-gical microscope was not employed and partialcerebellar resection was apparently carried out. It is

our experience that the difficulties Drs. Rougerie andGuyot had in locating the landmarks and the facialnerve within the internal auditory canal do notarise because of the magnification and visibilityprovided by microdissection.

Since submission of our manuscript, three addi-tional cases of acoustic neurinoma have been oper-ated upon by us with complete preservation of thefacial nerve in each instance.

REFERENCES

Bucy, P. C. (1951). Surgical treatment of acoustic tumours. J. Neuro-surg., 8, 547-555.

Cushing, H. (1917). Tumors of the Nervus Acusticus and the Syn-drome of the Cerebellopontile Angle. Saunders, Philadelphia.

Dandy, W. E. (1925). An operation for total removal of cerebello-pontine (acoustic) tumours. Surg. Gynec. Obstet., 41, 129-148.

- (1941). Results of removal of acoustic tumours by the unilateralapproach. Arch. Surg., 42, 1026-1033.

Dott, N. M. (1955). Discussion: Total removal of acoustic nervetumors. A.M.A. Arch. Neurol. Psychiat., 74, 454-455.

(1958). Facial paralysis-restitution by extra-petrous nerve graft.Proc. roy. Soc. Med., 51, 900-902.

Drake, C. G. (1960). Acoustic neuroma. Repair of facial nerve withautogenous graft. J. Neurosurg., 17, 836-842.

Horrax, G. (1950). A comparison ofresults after intracapsular enuclea-tion and total extirpation of acoustic tumours. J. Neurol.Neurosurg. Psychiat., 13, 268-70.

House, W. F. (1964). Transtemporal bone microsurgical removal ofacoustic neuromas. Arch. Otolaryng., 80, 599-676.

Kurze, T. (1958). UJnpublished data.Kurze, T., and Doyle, J. B. Jr. (1962). Extradural intracranial (middle

fossa) approach to the internal auditory canal. J. Neurosurg.,19, 1033-1037.

McKenzie, K. G., and Alexander, E. (1955). Acoustic neuroma.Clin. Neurosurg., 2, 21-36.

Mount, L. A. (1945). The lateral position for operations in the cere-bellopontine angle. J. Neurosurg., 2, 460-461.

Nielsen, A. (1942). Acoustic tumours, with special reference to end-results and sparing of the facial nerve. Ann. Surg., 115, 849-863.

Olivecrona, H. (1950). Analysis of results of complete and partialremoval of acoustic neuromas. J. Neurol. Neurosurg. Psychiat.,13, 271-2.

Panse, R. (1904). Klinische und pathologische Mitteilungen. IV.Ein Glioms des Akustikus. Arch. Ohrenheik., 61, 251-255.

Pool, J. L., and Pava, A. A. (1957). The Early Diagnosis and Treatmentof Acoustic Nerve Tumors. Thomas, Springfield, Illinois.

Rand, R. W. (1957). Hypothermia anesthesia in the sitting position.Report of two cases of acoustic neurinoma. J. Neurosurg.,14, 648-654.

Ransohoff, J., Potanos, J., Boschenstein, F., and Pool, J. L. (1961).Total removal of recurrent acoustic tumours. Ibid., 18, 804-810.

Revilla, A. G. (1947). Neurinomas of the cerebellopontile recess.A clinical study of 160 cases including operative mortality andend results. Bull. Johns Hopk. Hosp., 80, 254-296.

Rougerie, J., and Guyot, J. F. (1964). Essai de conservation du nerffacial dans l'ablation des neurinomes de l'angle ponto-c6r&-belleux. Neurochirg., 10, 13-21.

Scanlan, R. L. (1964). Positive contrast medium (iophendylate) indiagnosis of acoustic neuroma. Arch. Otolaryng., 80, 698-706.

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